1. Field of the Invention
The present invention relates to an ink jet ink and an ink jet recording method.
2. Description of the Related Art
It is generally known that a pigment alone is hardly dispersed in a dispersion medium. Accordingly, many studies have heretofore been made in order to obtain a stable pigment dispersion. In particular, in recent years, in an ink jet recording apparatus, which has been frequently used in an office or an ordinary home, a pigment ink having compounded therein the pigment as a coloring material has often been used. Accordingly, many studies have been made to improve ejection stability of the ink by dispersing the pigment in the dispersion medium and stabilizing the dispersion.
For example, there is a proposal of an ink using a water-soluble polymer obtained by polymerizing acryloylmorpholine as a dispersant for dispersing a water-insoluble colorant in an aqueous medium (see Japanese Patent Application Laid-Open No. H07-242849).
However, even in the case of using the water-soluble polymer proposed in Japanese Patent Application Laid-Open No. H07-242849 as a dispersant, it has been difficult to continuously eject an ink using a pigment having a secondary amino group in its structure as a coloring material, by an ink jet system in a stable manner. Among constituent members of an ink jet recording head, many of members to be brought into contact with the ink (liquid-contact members) have a negatively charged surface as a surface to be brought into contact with the ink (such as a liquid-contact surface or a nozzle surface). Accordingly, when the ink using a pigment having a secondary amino group in its structure is brought into contact with the liquid-contact member, ionic bonding is produced between the pigment and the liquid-contact member. This has caused a problem in that the ink is accumulated to cause clogging or the like, and hence it is difficult to perform continuous ejection in a stable manner.
It should be noted that the ink described in Japanese Patent Application Laid-Open No. H07-242849 uses an oil-soluble dye or carbon black as a water-insoluble coloring material. Accordingly, no dispersant capable of solving the above-mentioned problem has been designed. In addition, a polymer containing a unit derived from acryloylmorpholine, which polymer is used as a dispersant in the ink described in Japanese Patent Application Laid-Open No. H07-242849, has poor solubility in water. Accordingly, even in the case of using the polymer proposed in Japanese Patent Application Laid-Open No. H07-242849 as a dispersant, the pigment has not been able to be stably dispersed in the ink, and it has been difficult to continuously eject the ink in a stable manner.